Interferometric alignment of optical multicore fibers to be connected

ABSTRACT

The ends of sensing and interrogating multicore fibers are brought into proximity for connection in a first orientation with one or more cores in the sensing fiber being paired up with corresponding one or more cores in the interrogating fiber. Optical interferometry is used to interrogate at least one core pair and to determine a first reflection value that represents a degree of alignment for the core pair in the first orientation. The relative position is adjusted between the ends of the fibers to a second orientation. Interferometry is used to interrogate the core pair and determine a second reflection value that represents a degree of alignment for the core pair in the second orientation. The first reflection value is compared with the second reflection value, and an aligned orientation is identified for connecting the sensing and interrogating fibers based on the comparison.

RELATED APPLICATIONS

This application is the U.S. national phase of International ApplicationNo. PCT/US2016/024021 filed Mar. 24, 2016 which designated the U.S. andclaims priority to and the benefit of the filing date of U.S.Provisional Patent Application 62/139,096, entitled “INTERFEROMETRICALIGNMENT OF OPTICAL MUTICORE FIBERS TO BE CONNECTED,” filed Mar. 27,2015, the entire contents of each of which is are incorporated byreference.

TECHNICAL FIELD

The technology relates to optical fiber connections.

INTRODUCTION

Optical fibers contain one or more optical cores surrounded typically bycladding, a buffer material, and a jacket. Optical fibers need to beconnected accurately, reliably, and inexpensively. This is challengingfor optical fibers that contain multiple optical cores, referred to as a“multicore fiber,” because each of the corresponding cores should bealigned when two multicore fibers are connected. Even when the outersurfaces of the two multicore fibers, e.g., the ferrules covering thefibers, are aligned in a connector, the corresponding cores within theconnector for the two fibers may not be aligned or could be aligned moreaccurately. Small misalignments can adversely impact the amount of lighttransferred between the connected multicore fibers.

SUMMARY

Example embodiments of the technology described in this applicationrelate to a method for aligning one or more cores in a sensing multicoreoptical fiber with one or more cores in an interrogating multicoreoptical fiber. Each core in the sensing multicore optical fiber ispaired with a respective core in the interrogating multicore opticalfiber to form a core pair. Optical interferometry is used to interrogateat least one core pair through the interrogating core and to determine afirst reflection value from the sensing core in the core pair thatrepresents a degree of alignment for the core pair in a firstorientation. Optical interferometry is also used to interrogate the corepair through the interrogating core and to determine a second reflectionvalue from the sensing core in the core pair that represents a degree ofalignment for the core pair in a second orientation. An alignmentorientation for the core pair is identified based on the firstreflection value and the second reflection value.

The method may be performed for multiple core pairs.

The relative position between the ends of the sensing and interrogatingcores may be adjusted to the aligned orientation, and the sensingmulticore optical fiber connected to the interrogating multicore opticalfiber with the core pair in the alignment orientation. In one exampleimplementation, the first reflection value that represents a degree ofalignment for the core pair in the first orientation is compared withthe corresponding second reflection value that represents a degree ofalignment for the core pair in the second orientation, and the alignmentorientation for connecting the core pair is identified based on thecomparing. The adjusting may include rotation of one or both of thesensing core followed by interrogating core in the core pair.

In another example implementation, at least the ends of the sensing andinterrogating multicore fibers are placed in a groove of a structurewith the ends of the sensing and interrogating multicore fibers beingbrought into proximity for connection. One or both of the sensing andinterrogating multicore fibers is then rotated in the groove.

In another example implementation, the sensing multicore fiber isincluded in a first ferrule and the interrogating multicore fiber isincluded in a second ferrule. The adjusting includes rotation of one orboth of the first and second ferrules. At least the ends of the firstand second ferrules may be placed in a split sleeve connector, and oneor both of the first and second ferrules is/are rotated while the firstand second ferrules are in the split sleeve.

The optical interferometry may for example be optical frequency domainreflectometry (OFDR).

As described in more detail below, the sensing multicore optical fiberis associated with a surgical instrument an example application. OFDRsensing and processing of reflected light from the sensing multicoreoptical fiber is used to determine the position and/or shape of at leastsome portion of the surgical instrument.

In example implementations, the aligned orientation for connecting thecore pair is identified based on a largest minimum measured reflectionamplitude for the core pair and/or based on one or more of insertionloss and return loss for the core pair. The first and second reflectionvalues may be from Bragg gratings in the sensing core of the core pairand/or from Rayleigh scatter in the sensing core of the core pair.

Example embodiments of the technology described in this application alsorelate to an apparatus for aligning one or more cores in a sensingmulticore optical fiber and one or more cores in an interrogatingmulticore optical fiber, where each core in the sensing multicoreoptical fiber is paired with a respective core in the interrogatingmulticore optical fiber to form a core pair. An optical interferometeris configured to interrogate at least one core pair and to determine afirst reflection value from the sensing multicore optical fiber in thecore pair that represents a degree of alignment for the core pair in thefirst orientation. The optical interferometer is further configured tointerrogate the core pair through the interrogating core and todetermine a second reflection value from the sensing core in the corepair that represents a degree of alignment for the core pair in a secondorientation. Circuitry is configured to identify an alignmentorientation for the core pair based on the first reflection value andthe second reflection value.

An actuator is configured to adjust the relative position between theends of the sensing and interrogating multicore optical fibers to asecond orientation. A connector is configured to connect the sensingmulticore optical fiber to the interrogating multicore optical fiberwith the core pair in the alignment orientation. For example, theactuator may be configured to rotate one or both of the sensing andinterrogating multicore fibers.

In an example implementation, the apparatus includes a structure havinga groove, and wherein the actuator is configured to rotate one or bothof the sensing and interrogating multicore fibers while the sensing andinterrogating multicore fibers are in the groove.

In an example implementation, the apparatus includes a first ferruleincluding the sensing multicore fiber and a second ferrule including theinterrogating multicore fiber. The actuator is configured to rotate oneor both of the first and second ferrules. A split sleeve structure maybe used to encompass at least the ends of the first and second ferrulesconfigured to bring the ends of the sensing and interrogating multicorefibers into proximity for connection. In this example, the actuator isconfigured to rotate one or both of the first and second ferrules whilethe first and second ferrules are in the split sleeve.

Example embodiments of the technology described in this application alsorelate to a surgical system that includes a first multicore opticalfiber having one or more cores and a mounting interface for a surgicalinstrument. The surgical instrument includes a second multicore opticalfiber. Each core in the first multicore optical fiber is paired with arespective core in the second multicore fiber to form a core pair. Anoptical interferometer coupled to the first multicore fiber isconfigured to interrogate at least one core pair in a first orientationto determine a first reflection value from the second multicore opticalfiber in the core pair, and interrogate the core pair in a secondorientation to determine a second reflection value from the secondmulticore optical fiber in the core pair. The first and secondreflection values represent first and second degrees of alignment,respectively, for the core pair. A processor is configured to identifyan alignment orientation for the core pair based on the first reflectionvalue and the second reflection value.

In an example implementation, an actuator is configured to adjust therelative position between the ends of the first and second multicoreoptical fibers to a second orientation. A connector is configured toconnect the second multicore optical fiber to the first multicoreoptical fiber with the core pair in the alignment orientation. Theactuator may be configured to rotate one or both of the first multicoreoptical fiber and the second multicore optical fiber while the firstmulticore optical fiber and to the second multicore optical fiber are ina groove. Another alternative is to use a first ferrule including thefirst multicore optical fiber and a second ferrule including the secondmulticore optical fiber. The actuator is configured to rotate one orboth of the first and second ferrules. At least the ends of the firstand second ferrules may be placed in a split sleeve structure to bringthe ends of the first and second multicore optical fibers into proximityfor connection. In this case, the actuator is configured to rotate oneor both of the first and second ferrules while the first and secondferrules are in the split sleeve.

In an example implementation, the optical interferometer includes anoptical frequency domain reflectometer which is configured to sense andprocess reflected light from the second multicore optical fiber todetermine the position and/or shape of at least some portion of thesurgical instrument.

A method, apparatus, and surgical system as described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show cross-sections of misaligned multicore fibers to beconnected;

FIG. 2 shows an example v-shaped groove support for bringing twomulticore fibers into abutment for connection;

FIGS. 3A and 3B show a breakaway of both sides of the supported fibersfrom FIG. 2 indicating that rotation of at least one of the fibers isneeded for better core alignment;

FIG. 4 illustrates a non-limiting example embodiment for aninterferometrically-based multicore fiber alignment system;

FIG. 5 is a flowchart illustrating example procedures forinterferometrically-based multicore fiber alignment for connection;

FIG. 6 shows a non-limiting example embodiment using an OFDR-basedmulticore fiber alignment system;

FIG. 7 is a flowchart illustrating example procedures forinterferometrically-based multicore fiber alignment for connection forinterferometrically-based multicore fiber alignment system in FIG. 7;

FIG. 8 shows a non-limiting example embodiment in a surgical system;

FIG. 9A shows a multicore fiber in a ferrule with FIGS. 9B and 9Cshowing a side view of an exaggerated example of cleaved ends ofabutting misaligned multicore fibers to be connected in their respectiveferrules;

FIG. 10 shows non-limiting example details for mounting two multicorefibers for alignment in accordance with another example embodiment; and

FIGS. 11A-11E are example graphs of reflection v. distance showingiterative increasing alignment of two multicore fibers using the exampleOFDR-based multicore fiber alignment system.

DETAILED DESCRIPTION

The following description sets forth specific details, such asparticular embodiments for purposes of explanation and not limitation.But it will be appreciated by one skilled in the art that otherembodiments may be employed apart from these specific details. In someinstances, detailed descriptions of well known methods, interfaces,circuits, and devices are omitted so as not to obscure the descriptionwith unnecessary detail. Individual blocks are shown in the figurescorresponding to various nodes. Those skilled in the art will appreciatethat the functions of those blocks may be implemented using individualhardware circuits, using software programs and data in conjunction witha suitably programmed digital microprocessor or general purposecomputer, and/or using applications specific integrated circuitry(ASIC), and/or using one or more digital signal processors (DSPs).Software program instructions and data may be stored on anon-transitory, computer-readable storage medium, and when theinstructions are executed by a computer or other suitable processorcontrol, the computer or processor performs the functions associatedwith those instructions.

Thus, for example, it will be appreciated by those skilled in the artthat diagrams herein can represent conceptual views of illustrativecircuitry or other functional units. Similarly, it will be appreciatedthat any flow charts, state transition diagrams, pseudocode, and thelike represent various processes which may be substantially representedin computer-readable medium and so executed by a computer or processor,whether or not such computer or processor is explicitly shown.

The functions of the various illustrated elements may be providedthrough the use of hardware such as circuit hardware and/or hardwarecapable of executing software in the form of coded instructions storedon computer-readable medium. Thus, such functions and illustratedfunctional blocks are to be understood as being eitherhardware-implemented and/or computer-implemented, and thusmachine-implemented.

In terms of hardware implementation, the functional blocks may includeor encompass, without limitation, a digital signal processor (DSP)hardware, a reduced instruction set processor, hardware (e.g., digitalor analog) circuitry including but not limited to application specificintegrated circuit(s) (ASIC) and/or field programmable gate array(s)(FPGA(s)), and (where appropriate) state machines capable of performingsuch functions.

In terms of computer implementation, a computer is generally understoodto comprise one or more processors or one or more controllers, and theterms computer, processor, and controller may be employedinterchangeably. When provided by a computer, processor, or controller,the functions may be provided by a single dedicated computer orprocessor or controller, by a single shared computer or processor orcontroller, or by a plurality of individual computers or processors orcontrollers, some of which may be shared or distributed. Moreover, theterm “processor” or “controller” also refers to other hardware capableof performing such functions and/or executing software, such as theexample hardware recited above.

There are a variety of ways that two optical fibers may be connectedsuch as but not limited to mechanical splicing that holds the ends ofthe fibers together mechanically and fusion splicing that uses heat tofuse the ends of the fibers together. For purposes of the descriptionbelow, the term connector encompasses the variety of ways for toconnecting optical fibers.

FIGS. 1A and 1B show cross-sections of multicore optical fibers 10 and12 to be connected, each fiber having four optical cores A, B, C, and D.Although the non-limiting example in the description uses four cores forillustration, the technology set forth in the application applies to twocores, three cores, and greater than four cores. Even when the outersurfaces of the two multicore fibers 10 and 12, e.g., the ferrulescovering the fibers, are aligned for connection, the corresponding coresA-A, B-B, C-C, and D-D within or at the connection for the two fibersmay not be aligned or could be aligned more accurately. Smallmisalignments can adversely impact the amount of light transferredbetween the connected multicore fibers A-A, B-B, C-C, and D-D. FIG. 1Bshows a clockwise rotational misalignment around the center core A suchthat cores B-B, C-C, and D-D for multicore fibers 10 and 12 are notaligned.

FIG. 2 shows an example structure 14 with a V-shaped groove in which thetwo fibers may be placed for abutment of the connecting ends of thefibers 10 and 12. More particularly, the V-groove provides a fast,simple, and inexpensive structure for bringing two multicore fibers intoabutment for connection and typically with the center cores A-Areasonably accurately aligned. But one or more off-center core pairs,B-B, C-C, and D-D in the examples in FIGS. 1A, 1B and 2A and 2B, aremisaligned. The V-groove is an example of a groove. More generally, agroove encompasses a channel, a slot, a cut, a depression, and the like.

FIGS. 3A and 3B show a breakaway of both sides of the V-groove supportedfibers from FIG. 2 indicating that rotation of at least one of thefibers is needed for better core alignment for the off-center corepairs. When two multicore fibers are connected with misaligned corepairs, optical performance of the connected fiber decreasessignificantly, e.g., in term of insertion loss, return loss, etc. Thegroove alignment support is very low cost and advantageously provides away to align and connect the cores in optical fibers placed into thegroove without requiring the fibers to be encased in prealignedferrules. A non-limiting ferrule and fiber alignment and connectionexample embodiment is described below in conjunction with FIG. 10.

FIG. 4 illustrates a non-limiting example embodiment for aninterferometrically-based multicore fiber alignment system thatovercomes these alignment problems and improves the optical performanceof the connected fiber dramatically. This alignment system isparticularly advantageous when an optical interrogator is connected tothe optical fiber in normal use. In other words, since the opticalinterrogator is already present, using it to provide information aboutthe quality of the core alignment and/or connection does not add expenseor significant complexity to the system.

FIG. 4 is described in conjunction with the flowchart in FIG. 5illustrating example procedures for interferometrically-based multicorefiber alignment. First, the ends of the sensing and interrogatingoptical multicore fibers 10 and 12 are placed in a groove of structure14 into proximity for connection in a first orientation with cores inthe sensing multicore fiber being paired up with corresponding cores ina second multicore fiber, e.g., cores A-A are a core pair and cores B-Bare a core pair (step S1). The sensing fiber 10 in this example is on asensor or application side of the connection, and the interrogatingfiber 12 in this example is on an optical interrogator side of theconnection. An optical interferometer (an interferometric interrogationsystem 18 in the example embodiment of FIG. 4) interrogates one or morepairs of cores and determines a first value that represents a firstdegree of alignment for one of the one or more pairs of cores in thefirst orientation (step S2). Although multiple or even all of the pairsof cores may be interrogated and processed, satisfactory results may beobtained by interrogating just one radial core pair (other than thecenter core pair).

The relative position between the ends of two multicore fibers isadjusted to a second orientation via an actuator (step S3). In theexample embodiment of FIG. 5, the actuator is a fiber rotator 22controlled by a controller 20, which receives an output signal from theinterferometric interrogation system 18. Alternatively, a fiber rotatorbe used on the sensor side, or two fiber rotators could be used. Inaddition, the fiber rotator may be controlled by a signal directly fromthe interferometric interrogation system 18.

The optical interferometer subsequently interrogates the one or morepairs of cores and determines a second reflection value from the sensingmulticore optical fiber in the one pair of cores that represents adegree of alignment for the one pair of cores in the second orientation(step S4). The first reflection value that represents a degree ofalignment for the one pair of cores in the first orientation arecompared by a comparator with the corresponding second reflection valuethat represents a degree of alignment for the one pair of cores in thesecond orientation (step S5). The comparator could be a part of othercircuitry, part of the interferometric interrogation system 18, part ofthe controller 20, or even a standalone circuit. An alignmentorientation for connecting the two multicore fibers may then bedetermined based on the comparison (step S6). For example, theorientation with the greatest reflection value may be used.Alternatively, the process may repeat one or more times starting fromstep S3 until an orientation with a greatest reflection value isdetermined. Still further, the process may repeat one or more timesstarting from step S3 until a predetermined level of alignment accuracyis achieved. Ultimately, the fibers are connected at the orientationwith the desired alignment.

Typically, for fibers with a center core and one or more outer cores,the optical interrogator assesses the quality of the orientation and/orconnection between the outer cores of the connected multicore fiber. Theinterrogator may sense Bragg grating signal amplitude or Rayleighscatter amplitude from interrogated core pairs depending on the type ofsensor. In one example embodiment, the interrogator continuouslymeasures the amplitude of the measured light signal as the connectionfor one or more core pairs is adjusted. The connection adjustment thatproduces a largest minimum amplitude across all of the cores may be usedfor example because tests have shown that performance is oftencontrolled by the lowest performing core pair in a multicore fiber.

Increased optical fiber performance and/or robustness are benefits.Another benefit is that lower tolerance fiber connector can be used,(thereby reducing the cost and/or complexity of the connector), and thatlower tolerance compensated for using the adjustment capabilitydescribed above.

FIG. 6 shows a non-limiting example embodiment using an OpticalFrequency Domain Reflectometry (OFDR)-based multicore fiber alignmentsystem that finds advantageous example application to optical strainsensing. Optical strain sensing is useful for measuring physicaldeformation of a core caused by, for example, the change in tension,compression, or temperature of an optical fiber. A continuous measure ofstrain along the length of a core can be derived by interpreting theoptical response of the core using swept wavelength inteferometery.Optical time domain measurements with high resolution and highsensitivity may be achieved using Optical Frequency Domain Reflectometry(OFDR). These measurements enable several important fiber-optic sensingtechnologies, such as distributed strain sensing. Distributed strainmeasurements performed upon a multi-core optical fiber permitdetermination of a three dimensional position of the fiber as detailedin U.S. Pat. No. 8,773,650, the contents of which are incorporatedherein by reference. A multiple channel OFDR is connected to severalindependent optical or cores within the multi-core optical fiber. Thestrain responses of these cores (reflections from Bragg gratings in thecore and/or reflections Rayleigh scatter in the core) are simultaneouslymeasured as the fiber is placed in a given configuration. The relativepositions of the cores along the length of the multi-core optical fiberallow determination of a strain profile of the multi-core optical fiber.The strain profile may be used to determine the three dimensionalposition of the fiber, or one or more of the components (1)-(3) of thisprofile may be used independently.

An OFDR-based distributed strain sensing system includes a tunable lightsource 23, an interferometric interrogator 26, a laser monitor network28, an optical fiber sensor including an interrogator side fiber 12, aconnector 24, and a sensor side fiber 10, data acquisition electroniccircuitry 32, and a system controller data processor 30 as depicted inan example multi-channel OFDR system 21 in FIG. 6. Each channelcorresponds to a fiber core.

FIG. 7 is a flowchart illustrating example procedures forinterferometrically-based multicore fiber alignment and connection forinterferometrically-based multicore fiber alignment and connectionsystem in FIG. 6. The steps describe the operation for one core that isapplied to each of the cores in the multicore fiber.

During an OFDR measurement, a tunable light source 23 is swept through arange of optical frequencies (step S10). This light is split with theuse of optical couplers and routed to two separate interferometers 26and 28. The first interferometer 26 serves as an interferometricinterrogator and is connected via a connector 24 to a length ofmulticore sensing fiber. Light enters the multicore sensing fiber 10through the measurement arm of the interferometric interrogator 26 (stepS11). Scattered light from the sensing fiber 10 is then interfered withlight that has traveled along the reference arm of the interferometricinterrogator 26 (step S12). The laser monitor network 28 contains aHydrogen Cyanide (HCN) gas cell that provides an absolute wavelengthreference throughout the measurement scan (step S13). The secondinterferometer, within the laser monitor network 28, is used to measurefluctuations in tuning rate as the light source is scanned through afrequency range (step S14). A series of optical detectors (e.g.,photodiodes) convert the light signals from the laser monitor network,gas cell, and the interference pattern from the sensing fiber toelectrical signals (step S15). A data processor in a data acquisitionunit 32 uses the information from the laser monitor 28 interferometer toresample the detected interference pattern of the sensing fiber 10 sothat the pattern possesses increments constant in optical frequency(step S16). This step is a mathematical requisite of the Fouriertransform operation. Once resampled, a Fourier transform is performed bythe system controller 30 to produce a light scatter signal in thetemporal domain for an initial orientation of the multicore fibers 12 or10 (step S17). In the temporal domain, the amplitudes of the lightscattering events are depicted verses delay along the length of thefiber. Using the distance that light travels in a given increment oftime, this delay can be converted to a measure of length along thesensing fiber. In other words, the light scatter signal indicates eachscattering event as a function of distance along the fiber. The samplingperiod is referred to as the spatial resolution and is inverselyproportional to the frequency range that the tunable light source 23 wasswept through during the measurement.

One or both of the multicore fibers 12 or 10 is adjusted to a neworientation, e.g., rotated by fiber rotator 22 or by a ferrule rotatorsuch as that shown below in FIG. 10, and then the steps S10-S17 arerepeated (step S18). The scatter amplitudes for the initial orientationare compared to those for the new orientation (or the amplitudes for thetwo most recent orientations are compared) to determine if they arewithin an acceptable difference (step S19). If not, then the processreturns to step S18; if so, then the adjustment is complete (step S20),and the fibers are connected.

FIG. 8 shows a non-limiting example embodiment for a surgical system 800that includes a manipulator arm 810 on which a surgical instrument 850is removably mounted via a mounting interface 816. Mounting interface816 allows communication between surgical system 800 and instrument 850of power, data, control signals, and any other operative modalities. Alocal or remote user interface 802 allows a user to interact withsurgical system 800 and instrument 850.

Surgical system 850 further includes a multiple channel OFDR system 21coupled to an interrogating fiber 12 that terminates in a connector 812.Instrument 850 includes a sensing fiber 10 that terminates in aconnector 852 that mates with connector 812. Surgical system 850 alsoincludes an alignment actuator 814 that allows rotation of fiber 12 inresponse to measurements by multiple channel OFDR system 21 to align theinterrogator side and sensor side fibers for connection 24, as explainedin example embodiments above (in various embodiments, multiple channelOFDR system 21 can also be used to measure the shape of and/or strainassociated with surgical instrument 850 during clinical use).

In some embodiments, alignment actuator 814 can be an active adjustmentmechanism (e.g., a motorized system that adjusts the rotation ofinterrogating fiber 12 with respect to sensing fiber 10 in response tothe output of multiple channel OFDR system 21), and in otherembodiments, alignment actuator 814 can be a passive adjustmentmechanism (e.g., a manually adjustable structure that a user manipulatesin response to the output of multiple channel OFDR system 21). Invarious other embodiments, alignment actuator 814 can include bothautomated and manual adjustment capabilities.

While alignment actuator 814 is depicted on manipulator arm 810 forexemplary purposes, in various other embodiments, alignment actuator 814can be positioned anywhere on surgical system 800. In various otherembodiments, instrument 850 can additionally or alternatively includeits own alignment actuator 854 (active and/or passive) for adjusting therotation of sensing fiber 10 with respect to interrogating fiber 12.Note further that the particular routing and placement of sensing fiber10 and interrogating fiber 12 depicted in FIG. 8 is intended to beexemplary and not limiting. For example, in various embodiments, fiber12 can be routed on or within manipulator arm 810 or along any otherpath.

FIG. 9A shows a non-limiting example embodiment involving a multicorefiber in a ferrule. FIGS. 9B and 9C showing a side view of anexaggerated example of cleaved ends of abutting misaligned multicorefibers 10 and 12 to be connected in their respective ferrules 13 an 15.Ferrule mounted fibers are often angle polished to reduce reflectionwith ferrule and fiber end angles other than 90 degrees, e.g., 8 or 9degrees from vertical. Alignment of ferrule mounted fibers is also aproblem, even in the presence of the angle polish. Even when the outersurfaces of the angularly cleaved ferrules 13 and 15 are aligned forconnection and the center core pair A-A is aligned, the correspondingcore pairs B-B, C-C, and D-D for the multicore fibers 10 and 12 are notaligned, as indicated by the dashed lines. The amount of heightdisplacement is indicated with double-headed arrows. Accordingly, somerotation of the ferrule can improve the fiber connection.

FIG. 10 shows non-limiting details for an example connector forconnecting two multicore fibers embedded in their respective ferrulesfor alignment in accordance with another example embodiment. FIGS. 3Aand 3B above show a groove to initially align the center cores of twooptical fibers for connection without ferrules. FIG. 10 uses a splitsleeve connector because commercially available and inexpensive sapphireferrules and split sleeve connectors do a good job of aligning thecenter cores of multicore fibers that have center cores when the twoferrules are abutted together. This relatively cheap and easy splitsleeve connector restricts the active alignment to a single degree offreedom of the connector. A round ferrule 37 holds the interrogator sidemulticore fiber 10 precisely (e.g., +−<1 micron) in the center of a highprecision, preferably but not necessarily mass-produced split sleeve 36.The split sleeve is flexibly supported, e.g., by springs 38, so that itcan adjust position. The ferrule 37 for the multicore fiber 10 issolidly connected to a structure 40 with a relatively large flat surfaceto fix the rotational angle of the ferrule.

On the left side, there is a corresponding, rotatable ferrule 39 withinthe split-sleeve 36 that does not affect the split-sleeve connectoralignment of the center cores. The rotatable ferrule 39 contains thesensor side multicore fiber 12. Flexibly mounting the split-sleeve 36allows the split-sleeve 36 to reposition in space to accommodate the twoferrules 39 and 37. The ferrule 39 is rotated using a multi-linkuniversal joint 42 connected to a motor 44 that transmits torque andsome axial force. Although there is a space shown between the ferrules39 and 37, in practice they are moved into contact, e.g., by springsthat provide a compressional force on the sensor side. Once optimal corealignment is achieved, the two fibers may be connected.

FIGS. 11A-11E are example graphs of reflection v. distance showingiterative increasing alignment of two multicore fibers using the exampleOFDR-based multicore fiber alignment system. If the cores are not wellaligned, and reflection is measured as a function of distance along thecenter core and one outer core, the plot shown in FIG. 11A is producedwith the substantial amplitude difference shown. The dark waveformcorresponds to the reflected amplitude detected for the center core andthe lighter waveform corresponds to the reflected amplitude detected forone outer core. As the two multicore fibers are rotated towards closeralignment, the amplitude on the outer core (lighter waveform) getsprogressively larger as shown in FIGS. 11B-11D. FIG. 11E signals that adesired alignment is achieved, e.g., when the two waveforms have aboutthe same average amplitude.

Although various embodiments have been shown and described in detail,the claims are not limited to any particular embodiment or example. Noneof the above description should be read as implying that any particularelement, step, range, or function is essential such that it must beincluded in the claims scope. The scope of patented subject matter isdefined only by the claims. The extent of legal protection is defined bythe words recited in the allowed claims and their equivalents. Allstructural and functional equivalents to the elements of theabove-described preferred embodiment that are known to those of ordinaryskill in the art are expressly incorporated herein by reference and areintended to be encompassed by the present claims. Moreover, it is notnecessary for a device or method to address each and every problemsought to be solved by the technology described, for it to beencompassed by the present claims. No claim is intended to invokeparagraph 6 of 35 USC § 112 unless the words “means for” or “step for”are used. Furthermore, no embodiment, feature, component, or step inthis specification is intended to be dedicated to the public regardlessof whether the embodiment, feature, component, or step is recited in theclaims.

The invention claimed is:
 1. A method for aligning a sensing core in asensing multicore optical fiber with an interrogating core in aninterrogating multicore optical fiber, where the sensing core in thesensing multicore optical fiber is paired with the interrogating core inthe interrogating multicore optical fiber to form a core pair, themethod comprising: using optical interferometry to interrogate the corepair through the interrogating core and to determine a first reflectionvalue from the sensing core, wherein the first reflection valuerepresents a degree of alignment for the core pair in a firstorientation; using optical interferometry to interrogate the core pairthrough the interrogating core and to determine a second reflectionvalue from the sensing core, wherein the second reflection valuerepresents a degree of alignment for the core pair in a secondorientation; and identifying an alignment orientation for the core pairbased on the first reflection value and the second reflection value. 2.The method in claim 1, further comprising: adjusting a relative positionbetween an end of the sensing core and an end of the interrogating coreto the alignment orientation, and connecting the sensing multicoreoptical fiber to the interrogating multicore optical fiber with the corepair in the alignment orientation.
 3. The method in claim 2, whereinidentifying an alignment orientation for the core pair based on thefirst reflection value and the second reflection value comprises:comparing the first reflection value that represents the degree ofalignment for the core pair in the first orientation with the secondreflection value that represents the degree of alignment for the corepair in the second orientation; and identifying the alignmentorientation for connecting the core pair based on the comparing.
 4. Themethod in claim 2, further comprising: placing at least the ends of thesensing and interrogating multicore optical fibers in a groove of astructure, bringing the ends of the sensing and interrogating multicoreoptical fibers into proximity for connection, and rotating one or bothof the sensing and interrogating multicore optical fibers in the groove.5. The method in claim 2, wherein the sensing multicore optical fiber isincluded in a first ferrule and the interrogating multicore opticalfiber is included in a second ferrule, and wherein the adjustingincludes rotation of one or both of the first and second ferrules, themethod further comprising: placing at least ends of the first and secondferrules in a split sleeve connector and rotating one or both of thefirst and second ferrules while the first and second ferrules are in thesplit sleeve connector.
 6. The method in claim 1, wherein the opticalinterferometry includes optical frequency domain reflectometry (OFDR),wherein the sensing multicore optical fiber is associated with aninstrument, and wherein OFDR sensing and processing of reflected lightfrom the sensing multicore optical fiber is used to determine at leastone of: a position and a shape of at least a portion of the instrument.7. The method in claim 1, wherein the identifying step includesidentifying the alignment orientation for connecting the core pair basedon: a largest minimum measured reflection amplitude for the core pair orone or more of insertion loss and return loss for the core pair.
 8. Themethod in claim 1, wherein the first and second reflection values arefrom at least one of Bragg grating reflections and Rayleigh scatter inthe sensing core of the core pair.
 9. An apparatus for aligning asensing core in a sensing multicore optical fiber and an interrogatingcore in an interrogating multicore optical fiber, where the sensing corein the sensing multicore optical fiber is paired with the interrogatingcore in the interrogating multicore optical fiber to form a core pair,the apparatus comprising: an optical interferometer configured tointerrogate the core pair and to determine a first reflection value fromthe sensing multicore optical fiber in the core pair, wherein the firstreflection value represents a degree of alignment for the core pair in afirst orientation; the optical interferometer further configured tointerrogate the core pair through the interrogating core and todetermine a second reflection value from the sensing core in the corepair, wherein the second reflection value represents a degree ofalignment for the core pair in a second orientation, and circuitryconfigured to identify an alignment orientation for the core pair basedon the first reflection value and the second reflection value.
 10. Theapparatus in claim 9, further comprising: an actuator configured toadjust a relative position between an end of the sensing core and an endof the interrogating core to the alignment orientation, and a connectorconfigured to connect the sensing multicore optical fiber to theinterrogating multicore optical fiber with the core pair in thealignment orientation.
 11. The apparatus in claim 10, wherein thecircuitry is configured to identify the alignment orientation for thecore pair based on the first reflection value and the second reflectionvalue by: comparing the first reflection value that represents a degreeof alignment for the core pair in the first orientation with the secondreflection value that represents a degree of alignment for the core pairin the second orientation; and identifying the alignment orientation forconnecting the core pair based on the comparison.
 12. The apparatus inclaim 10, further comprising a structure having a groove, and whereinthe actuator is configured to rotate one or both of the sensing andinterrogating multicore optical fibers while the sensing andinterrogating multicore optical fibers are in the groove.
 13. Theapparatus in claim 10, further comprising a first ferrule for thesensing multicore optical fiber and a second ferrule for theinterrogating multicore optical fiber, wherein the actuator isconfigured to rotate one or both of the first and second ferrules; and asplit sleeve structure for at least a first end of the first ferrule anda second end of the second ferrule, the split sleeve structureconfigured to bring the ends of the sensing and interrogating multicoreoptical fibers into proximity for connection, wherein the actuator isconfigured to rotate one or both of the first and second ferrules whilethe first and second ferrules are in the split sleeve structure.
 14. Theapparatus in claim 9, wherein the optical interferometer includes anoptical frequency domain reflectometer, wherein the sensing multicoreoptical fiber is associated with an instrument, and wherein the opticalfrequency domain reflectometer is configured to sense and processreflected light from the sensing multicore optical fiber to determine atleast one of: a position and a shape of at least a portion of theinstrument.
 15. The apparatus in claim 9, wherein the circuitry isconfigured to identify the alignment orientation based on a largestminimum measured reflection amplitude for the core pair.
 16. Theapparatus in claim 9, wherein the circuitry is configured to identifythe alignment orientation based on one or more of insertion loss andreturn loss for the core pair.
 17. The apparatus in claim 9, wherein thefirst and second reflection values are from at least one of Bragggrating reflections and Rayleigh scatter in the sensing core of the corepair.
 18. A surgical system comprising: a first multicore optical fiberhaving one or more cores, a mounting interface for a surgicalinstrument, the surgical instrument comprising a second multicoreoptical fiber, wherein each core of the one or more cores in the firstmulticore optical fiber is paired with a respective core in the secondmulticore optical fiber to form one or more core pairs, an opticalinterferometer coupled to the first multicore optical fiber andconfigured to, for each core pair of the one or more core pairs:interrogate the core pair in a first orientation to determine a firstreflection value from the second multicore optical fiber in the corepair, and interrogate the core pair in a second orientation to determinea second reflection value from the second multicore optical fiber in thecore pair, wherein the first reflection value represents a first degreeof alignment for the core pair, and wherein the second reflection valuerepresents a second degree of alignment for the core pair, and aprocessor configured to, for each core pair of the one or more corepairs, identify an alignment orientation for the core pair based on thefirst reflection value of the core pair and the second reflection valueof the core pair.
 19. The surgical system in claim 18, furthercomprising: an actuator configured to adjust a relative position betweenan end of the first multicore optical fiber and an end of the secondmulticore optical fiber to an orientation based on the alignmentorientation of the one or more core pairs, and a connector configured toconnect the second multicore optical fiber to the first multicoreoptical fiber with the core pair in the orientation.
 20. The surgicalsystem in claim 19, wherein the processor is configured to, for eachcore pair of the one or more core pairs: compare the first reflectionvalue that represents a degree of alignment for the core pair in thefirst orientation with the corresponding second reflection value thatrepresents a degree of alignment for the core pair in the secondorientation; and identify the orientation for connecting the secondmulticore optical fiber to the first multicore optical fiber based onthe comparison.
 21. The surgical system in claim 19, wherein theactuator is configured to rotate one or both of the first multicoreoptical fiber and the second multicore optical fiber while the firstmulticore optical fiber and the second multicore optical fiber are in agroove.
 22. The surgical system in claim 19, further comprising: a firstferrule for the first multicore optical fiber and a second ferrule forthe second multicore optical fiber, wherein the actuator is configuredto rotate one or both of the first and second ferrules; and a splitsleeve structure for at least an end of the first ferrule and an end ofthe second ferrule, the split sleeve structure configured to bring theends of the first and second multicore optical fibers into proximity forconnection, wherein the actuator is configured to rotate one or both ofthe first and second ferrules while the first and second ferrules are inthe split sleeve structure.
 23. The surgical system in claim 18, whereinthe processor is configured to, for each core pair of the one or morecore pairs, identify the alignment orientation based on: a largestminimum measured reflection amplitude for the core pair, or one or moreof insertion loss and return loss for the core pair.